Metabolism of 1,25-dihydroxyvitamin D₃

This review summarizes what is known about the mechanisms by which plasma levels of 1,25-dihydroxyvitamin D₃[1,25(OH)₂D₃], a major calcium-controlling hormone, are regulated. Only a brief review of the regulation of 1,25(OH)₂D₃ synthesis is given, because this topic has already been reviewed extensively. Instead, the author discusses the mechanisms by which 1,25(OH)₂D₃ is metabolized to other compounds and the regulation of such metabolic processes. The catabolism of 1,25(OH)₂D₃ is important because tissue levels of any substance depend on both its rate of formation and its rate of metabolism to other substances.